Valve's Steam Dev Days summit is taking place in Seattle, Washington this week. The press wasn't invited, and while Valve promises to release video of the event in the coming weeks, news is already trickling out via social media—mostly Twitter. Steam Database has a good summary of what's been revealed thus far.

Some of the most interesting news involves the Steam controller. Valve's initial plans called for a touchscreen to sit between the controller's dual touchpads, but the company has decided to replace that touchscreen with a traditional D-pad and four-button combo. "Ghost mode" apparently makes the touchscreen redundant by providing a measure of on-screen mapping information. The buttons should be better for compatibility with older games, too, and they're likely cheaper to implement. A couple of pictures of the latest prototype are available here and here.

Valve told attendees that the Steam controller API supports up to 16 gamepads simultaneously, which has intriguing implications for local co-op. The fact that this is part of the API may mean third-party gamepads will get to participate in 16-controller action, as well. Valve has already expressed an interest in having hardware makers produce Steam controllers of their own.

AA batteries will reportedly provide power to the retail version of Valve's controller, giving gamers the freedom to use their own rechargeables. There's no indication that batteries can be charged using the controller, however. I wonder if it's possible to at least power the unit with a wired USB connection.

Although most developers tweeting from the event have been pretty positive, Ben Sullivan of United Front Games noticed "significant lag" in the game streaming demo he received. In-home streaming "isn't ready yet," he tweeted, adding that it's still a work in progress. Valve representatives told Sullivan that the streaming system is entirely software-based right now. However, it sounds like Valve plans to add hardware-accelerated video encoding and decoding. This hardware assist should reduce lag, Sullivan says.

Most of the Dev Days commentary has come from developers, but Valve actually put out some official news in a press release. In the last three months, the company says the number of active Steam users has grown by 15%, bringing the total to 75 million. The recent holiday sales no doubt contributed to that growth. There are clearly many developers interested in Valve's plans, too: 1200 attendees showed up for the event. Each one of them is reportedly walking away with a Haswell GT3e-powered Gigabyte Brix Pro small-form-factor system in addition to a Steam controller.